This invention pertains generally to the field of core drilling and more specifically to core drilling systems.
A sample of earth or rock taken from a bore hole in the earth is termed a xe2x80x9ccore samplexe2x80x9d in the fields of resource exploration and civil engineering. The core sample is used to determine the characteristics of a strata of earth or rock. A mining engineer may use a core sample to determine the extent of an ore vein, a petroleum engineer may use a core sample to determine the likelihood of finding recoverable petroleum in a strata, and a civil engineer may use a core sample to determine the strength of the bedrock underneath a large structure. Core drilling can be distinguished from borehole drilling in that the purpose of borehole drilling is to create a borehole through the earth but the purpose of core drilling is to create and retrieve a clean core sample from the length of a borehole.
A typical core bit used to collect a core sample is a hollow cylinder with a cutting surface on one face of the hollow cylinder. The core bit is fixedly attached on one end of a cylindrical pipe and inserted into a previously drilled bore hole. New sections of pipe are added to the upper end of the original pipe, creating a series of connected pipes in what is termed a drill stem, as the core bit is pushed into the borehole. Each section of pipe is on the order of 10 feet long. When the core bit reaches the bottom of the borehole, the core bit is forced against a rock strata as the core bit is rotated by rotating the drill stem. The combination of the force and the rotating cutting surface cuts a cylindrical core sample from the rock strata. The core sample is captured in an interior portion of the drill stem behind the core bit until the core sample can be retrieved from the borehole. The length of an interior tube containing a core barrel is typically five feet to 30 feet in length.
It is desirable to operate the core bit with as few changes in rotational speed and applied force as possible. An ideal operational mode for a core bit would allow the collection of a core sample without any changes in rotational speed or applied force. However, real world applications typically involve changes in both parameters while obtaining a core sample. Prior art core drilling apparatuses involve a chuck through which the drill stem passes. The chuck is movably attached to a stationary drilling platform. The chuck is typically used to apply longitudinal and rotary forces to the drill stem in order to advance the core bit. As the chuck has a limited amount of longitudinal movement, the chuck must be repositioned on a frequent basis in order to advance the core bit for the entire length of a core sample. This constant repositioning of the chuck results in numerous changes in the longitudinal and rotary forces applied to the drill stem during the course of collecting a core sample.
A core drilling system, as disclosed in U.S. Pat. No. 3,708,020, issued to Adamson, includes a continuous feed drill assembly employing upper and lower chucks. Each chuck has a hydraulic motor for suppling of rotary motion to a drill stem via a chuck. Each chuck also uses a plurality of hydraulic cylinders to move the chucks longitudinally in alternate fashion. Thus, the upper and lower chucks of the Adamson system provide a continuous drilling motion to a drill stem. However, the operation of the hydraulically powered and actuated chucks is not well coordinated because the hydraulic control system disclosed by Adamson is incapable of fully synchronizing the upper and lower chucks. This lack of synchronization can cause the continuous feed drill assembly to apply an inconsistent drilling force and speed to the drill stem. The Adamson system also relies on limit switches to switch the roles of the two chucks, further contributing to fluctuations in the speed of the drill stem.
In one aspect of the invention, a method is provided for operating by a controller a continuous feed drill head assembly including a plurality of chucks. The controller closes an open and retracted first chuck on a drill stem and begins advancing the first chuck. The controller repeats the following steps in order to generate a continuous drilling motion. The controller determines the linear velocity of the first chuck and synchronizes the linear velocity of a retracted second chuck with the linear velocity of the first chuck. The controller closes the second chuck on the drill stem and opens the first chuck, freeing the first chuck to move without affecting the drill stem. The controller retracts the first chuck while advancing the second chuck. The controller determines the linear velocity of the second chuck and synchronizes the linear velocity of the first chuck with the linear velocity of the second chuck. The controller closes the first chuck on the drill stem and opens the second chuck, freeing the second chuck to move without affecting the drill stem. The controller retracts the second chuck while advancing the first chuck.
In another aspect of the invention, a continuous feed drilling system is provided. The continuous feed drilling system includes a rotary drive. First and second chucks are slidably coupled to the rotary drive. First and second linear actuators are operable to slidably move respectively the first and second chucks in relation to the rotary drive. First and second linear transducers are operably coupled to the first and second chucks. A controller is operatively coupled to the first and second chucks, the first and second linear actuators, and the first and second linear transducers. The controller is programmed to synchronize the first and second chucks using signals received from the first and second linear transducers.
In another aspect of the invention, the controller of the continuous feed drilling system is further programmed to repetitively determine a linear velocity of a closed chuck, synchronize the linear velocity of an open chuck with the linear velocity of the closed chuck, close the open chuck and open the previously closed rotary, and simultaneously advance the closed chuck while retracting the open chuck.